BIST (built-in self test) circuitry provides a means of testing integrated circuits after manufacture. BIST circuitry is implemented on-chip and thus generally forms part of the final product. It allows test signals to be generated and applied to parts of a circuit under test (CUT), and the results verified automatically on-chip.
Analogue parts of integrated circuits are far more costly to test than the digital parts, due in part to the continuous range of values of the input signals that should be tested. Thus, while analogue parts of integrated circuits usually form only 10-15% of the total area, testing these parts can account for over 50% of the testing cost, which includes the cost of providing test equipment capable of generating the necessary test sequences, and the time required for performing the tests.
ADCs are an example of an analogue component that is often found in the analogue part of integrated circuits, and Sigma-delta ADCs are a popular choice of ADC due to their relatively low quantization noise and low cost in terms of chip area. However, testing a sigma-delta ADC involves applying a high resolution test signal, the values of which should generally be 2 to 3 bits larger than the resolution of the converter, such that any distortion measured at the output originates only from the CUT. Therefore, a sophisticated waveform generator is usually required. Furthermore, advances in sigma-delta ADCs has enabled them to have increased dynamic ranges, and thus the test signal should be capable of testing over these higher ranges. There is a problem in providing a solution that can be implemented as a BIST and that meets these requirements.